1. Field of the Invention
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred onto all or part of the substrate (e.g., a glass plate), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate.
Instead of a circuit pattern, the patterning device can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can be a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate is typically rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through a beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
In an apparatus using an array of individually controllable elements, the array may include a very large number of individually controllable elements, and each of the individually controllable elements may be very small. Accordingly, it is difficult to manufacture an array of individually controllable elements that is precisely as designed. For example, some of the individually controllable elements, which may, for example, be rotatable mirrors, may be partially deformed. In addition, the response of each individually controllable element to a control voltage that may be used to control the individually controllable element may vary from element to element. Accordingly, it has previously been known that it is necessary to determine the characteristics of each of the individually controllable elements within an array, for example to determine its reflectivity to the radiation to be used in the lithographic apparatus and to determine the response of each of the individually controllable elements to a control voltage in order to provide calibration data that enables the array of individually controllable elements to be provided with the control signals necessary to provide a desired pattern.
For example, it has previously been known to inspect each individually controllable element within an array of individually controllable elements, for example using an interferometer, in order to determine its properties and to repeat the inspection of each individually controllable element while providing it with a plurality of different control voltages in order to calibrate its response to the control voltages. However, inspecting each individually controllable element and determining its individual response to a control voltage is time-consuming. This is particularly disadvantageous because the response of the individually controllable elements to respective control voltages may vary during the lifetime of the array of individually controllable elements. Accordingly, the calibration process may need to be repeated. The time required for subsequent calibration may result in increased costs of ownership of the lithography apparatus because, during the calibration process, the lithographic apparatus cannot be used to manufacture devices on a substrate.
Furthermore, the additional components required to provide a device to inspect the array of individually controllable elements may increase the cost of the lithographic apparatus. Alternatively, if the device for inspecting the array of individually controllable elements is not part of the lithographic apparatus, the calibration process may include the removal of the array of individually controllable elements from the lithographic apparatus in order to inspect it. Such an arrangement further increases the delay caused by a calibration process, further increasing the cost of ownership of the lithographic apparatus.